1. Field of the Invention
This invention generally relates to extra-corporeal, blood handling machines which are connected to the blood stream to process blood outside the body and, more specifically, it relates to the interconnections between flexible components which are used to contain blood flow such as blood tubing and the connectors which are used in blood handling machines such as ventricular assist, artificial kidney and heart-lung machines.
2. Description of the Prior Art
A serious problem plagues extra-corporeal, blood handling machines. While circulating blood, the machines tend to generate dangerous blood cell aggregates such as clots in areas of blood stasis and thrombi in areas of flow disturbances. (For the purposes of this application, the terms clot and thrombus will be used interchangeably.) The problem is serious because the presence of small blood clots within the human cardiovascular system can seriously impair the patient, resulting in strokes, organ impairment and even death.
The medical community is aware that the connectors that connect blood tubing to other components in the blood circuits involving these machines have been a primary site of blood clot generation. In an effort to solve the clotting problem which exists at those junctions, two different but related avenues of research have been pursued. Both avenues concern the blood compatibility of blood contacting surfaces. However, neither avenue has produced satisfactory results. Therefore, an acceptable solution to the blood clotting problem at the junctions has remained elusive.
One avenue of research has involved efforts to create an environment in the blood tubing connectors which simulates the environment found in the living body. The blood vessels of the body are coated with an intima consisting of an endothelial lining backed by connective tissue. Since blood clotting is not a problem along the intact intima, a segment of the medical community has believed that it can solve the clotting problem by encouraging pseudo intimas to grow on the inner surfaces of the connectors. This approach has had limited success but it also has presented other unacceptable problems. Once a pseudo intima is established, it may fail by delaminating from the substrate. If the pseudo intima does not delaminate, it continues to grow thicker with time. However, since the pseudo intima does not have its own blood vessels, the base layers eventually die and slough off into the blood flow. In either case, the deterioration of the pseudo intima presents a problem as serious as the blood clots.
Another avenue of research has focused on an effort to find better blood-compatible materials out of which connectors and tubing can be constructed. An underlying rationale for this approach is that the chemical composition of the connector materials elicits the clotting problem. In this search, thousands of materials have been examined for better blood-compatibility. As of yet, however, better materials have not been found which alone solve the clotting problem.
Since no satisfactory way has been found to eliminate the sources of blood clots around the tubing-connectors, two methods have been used to remove the clots before they cause serious damage. One method filters the clots out of the blood after it passes through the machine; the other method dissolves the clots by administering anticoagulants. Both methods are unsatisfactory solutions to the problem. Removal of blood clots through filtering tends to activate clotting mechanisms within the filter itself and generate other clots which threaten harm to the patient. The alternative of dissolving clots with anticoagulants forces the doctor to delicately balance two life-threatening phenomena. Administering too much anticoagulant can cause spontaneous internal bleeding, especially in the patients that may be platelet depleted; whereas administering too little will not effectively eliminate the clots. It is difficult to arrive at a dosage that avoids both problems.